Yarn-tying knots of the aforedescribed type of spinning, spooling and twisting machines are made by mechanical means which generally comprise a guide or support device into which the two parallel thread ends are laid and so disposed that the parallel yarn ends span between the guides of this structure. The knotter can have a beak which engages the stretch of the two yarns between the guides and has a hook which is fixed to a shaft upon which the beak is mounted, and a movable shear half which can function as a clamping member and which is pivotal on the beak. In these systems, the engagement by the beak of the afore-mentioned stretch of parallel yarn ends enables rotation of the beak to form a loop and twist the loop through at least two turns, whereupon the gripper formed between the movable half and the fixed half of the beak can engage the one of the yarn ends which is to be drawn through the loop.
The opening and closing of the beak are controlled by a relatively complex arrangement in the knotter.
Spooling frames generally comprise a large number of spooling stations from which the cops or bobbins holding the yarn must be replaced when empty with new cops or bobbins on the respective spindles.
The free ends of the yarn which have left the cops are held by thread brakes and must be tied to the new thread or yarn of the replacement cop or bobbin by a knotting operation.
As noted, the preferred knot for this purpose is the so-called catshead knot which has also been termed a chain-toggle knot, a chain knot or a form of bowline and characterized by its simplicity and ease of formation, but possibly of greatest importance, by its small bulk so that the knot does not interfere with spooling operations. During the formation of the knot, moreover, minimal tension increases are generated in the yarn and the same applied to any knotting of excess yarn from the knot.
The simplicity of this knot which substantially involves the formation of a loop and the twisting of this loop through at least two turns before the free ends of the two strands is drawn through the loop, makes the knot especially advantageous for production by knotting machines or mechanisms.
The mechanism previously described, therefore, is comparatively simple and can be easily controlled.
The opening of the beak, however, requires a stationary member in prior art structures and for closing the blade member to thereupon sever the excess yarn. While this arrangement creates fabrication problems, it has the more significant disadvantage that with each rotation of the beak shaft the blade must open and close and because of this an additional gripper must be provided to hold the yarn ends out of engagement by the blade or in the opening between the blade and the fixed beak member when the turns are journaled to twist the loop before the free ends of the yarn ends are engaged. Consequently, the apparatus is of a relatively complex construction in spite of the fact that a comparatively simple means is provided for opening and closing the beak.
It has already been proposed to provide a movable control member for the opening and closing of the beak, this member being designed to open the beak only when the member is shifted into the operating position. This earlier control member is provided as a transverse element between two parallel pivoting arms which are pressed against the cam by spring force, the cam controlling the points in time at which the beak is to open and close.
Since the pivotal arms must describe a circular path about their respective pivot axes, the control member has a corresponding arcuate movement. The control member is thereby tilted with respect to the end or ends of the movable shear half to be engaged thereby. Because of this the sliding engagement of the control end of the shear half and the control member, considering the fabrication and mounting tolerance, satisfactory control of the beak is only achieved when the contact points are fabricated with precision. Since the cam and the arms control thereby are only in force-transferring contact and because the mountings of the pivot axes generally are located where they cannot be massive in nature, even after a limited operational time, especially when thick or dense yarns are cut with the considerable force thereby required, deformation and wear occurs so that the blade does not close properly and both the clamping effect desired and the shear effects are lost.